As toners for developing electrostatic latent images in electrophotography and the like, there have been widely used those obtained by granulating compositions comprising a fixing resin medium such as a thermoplastic resin, a colorant such as carbon black dispersed in the resin medium and other property-imparting agents.
It has heretofore been used, as a preparation process of toners, to add a pigment such as carbon black and/or magnetic powder, a dye suitable for use in charge-controlling as needed, etc. to a fixing thermoplastic resin composed of a natural or synthetic polymer, premix the resulting mixture by a mixer, melt and knead it in a heated kneader such as a hot mill or extruder so as to disperse the pigment and dye in the resin, cool the dispersion, granulate it coarsely and then finely, and then classify the resulting particles so as to provide particles having a desired particle size.
However, such a preparation process is complicated in process and is insufficient in uniform dispersibility though it requires a long-time kneading at an elevated temperature in order to enhance the dispersibility of the pigment in the resin. It is hence difficult to obtain a toner having uniform electric and magnetic properties and satisfactory developability.
On the other hand, it has been proposed, as a process for directly providing a toner without using any grinding processes, to add a pigment and dye to at least one polymerizable monomer, emulsion- or suspension-polymerize the monomer so as to form a finely divided resin containing the pigment and dye, and then wash and dry the resulting fine particles (for example, Japanese Patent Publication No. 10231/1961, U.S. Pat. Nos. 3,391,082 and 3,634,251).
However, this process often encounters the following problem. Namely, since the magnetic powder and pigment having hydrophilic surface characteristics are poor in wettability to the monomer, it is difficult to uniformly disperse them in the monomer and further in the resulting particles. Therefore, it is only possible to obtain a toner poor in electric properties because most of the pigment and magnetic powder adhere on the surfaces of the resulting particles.
In order to solve such a problem, it has been conducted to disperse carbon black and the like in a monomer in the presence of an organic titanate coupling agent (Japanese Patent Application Laid-Open No. 158650/1983) or to subject likewise a pigment such as carbon black and magnetic powder to a surface treatment with a silane coupling agent, titanium coupling agent, aluminum coupling agent or the like. It has however been impossible to attain sufficient effects therefrom.